Copper(II) Schiff base complex derived from salen ligand: structural investigation, Hirshfeld surface analysis, anticancer and anti-SARS-CoV-2.

This work deals with the synthesis and characterization of copper(II) complex [Cu(salen)(H2O)](1) of salen-type Schiff base ligand derived from the condensation of 5-bromo-2-hydroxy-3-methoxybenzaldehyde and ethylenediamine in EtOH. This complex was characterized by different spectroscopic and physicochemical methods. Single crystal X-ray crystallography study revealed that Cu(II) in complex (1) is five-coordinate and adopts a distorted square pyramidal geometry. A DFT calculation was employed to evaluate the optimized electronic structure, HOMO-LUMO, energy gap, and global parameters. A detailed structural and non-covalent interaction on the complex is investigated by single crystal structure analysis and computational approaches. The strength of the interaction and 3D topology of the crystal packing are visualized through an energy framework. Hirshfeld surface and 2D fingerprint plots have been explored in the crystal structure of the complex. The anticancer properties of copper(II) complex was studied against the selected cancerous cell lines of breast cancer, cervical cancer, colon cancer and hepatocellular carcinoma. Additionally, molecular docking and MD simulations was performed on the complex to predict the binding mode and interactions between the ligand and the main protease of the SARS-CoV-2 (PDB ID: 7CBT and 7D1M). The molecular docking calculations of the complex (1) with SARS-CoV-2 virus revealed the binding energy of -8.1 kcal/mol and -7.5 kcal/mol with an inhibition constant of 3.245 µM and 2.318 µM at inhibition binding site of receptor towards 7CBT and 7D1M main protease (Mpro), respectively. Besides this, molecular docking results (-7.6 kcal/mol, 3.196 µM) towards Escherichia coli PBP2 targets (PDB ID: 6G9S) was also studied. Communicated by Ramaswamy H. Sarma.

Contribution of the catalytic dyad of SARS-CoV-2 main protease to binding covalent and noncovalent inhibitors.

The effect of mutations of the catalytic dyad residues of SARS-CoV-2 main protease (MProWT) on the thermodynamics of binding of covalent inhibitors comprising nitrile [nirmatrelvir (NMV), NBH2], aldehyde (GC373), and ketone (BBH1) warheads to MPro is examined together with room temperature X-ray crystallography. When lacking the nucleophilic C145, NMV binding is ∼400-fold weaker corresponding to 3.5 kcal/mol and 13.3 °C decrease in free energy (ΔG) and thermal stability (Tm), respectively, relative to MProWT. The H41A mutation results in a 20-fold increase in the dissociation constant (Kd), and 1.7 kcal/mol and 1.4 °C decreases in ΔG and Tm, respectively. Increasing the pH from 7.2 to 8.2 enhances NMV binding to MProH41A, whereas no significant change is observed in binding to MProWT. Structures of the four inhibitor complexes with MPro1-304/C145A show that the active site geometries of the complexes are nearly identical to that of MProWT with the nucleophilic sulfur of C145 positioned to react with the nitrile or the carbonyl carbon. These results support a two-step mechanism for the formation of the covalent complex involving an initial non-covalent binding followed by a nucleophilic attack by the thiolate anion of C145 on the warhead carbon. Noncovalent inhibitor ensitrelvir (ESV) exhibits a binding affinity to MProWT that is similar to NMV but differs in its thermodynamic signature from NMV. The binding of ESV to MProC145A also results in a significant, but smaller, increase in Kd and decrease in ΔG and Tm, relative to NMV.

Ultrasound assisted regioselective synthesis of novel adamantyl-pyrazolo[1,5-a]pyrimidines in aqueous media and molecular docking and drug likeness studies

Multi-step synthesis of adamantyl-pyrazolo[1,5-a]pyrimidine derivatives under ultrasound irradiation has been described adopting the technique of molecular hybridization, whereby two core bioactive units- adamantanamine and pyrazolo[1,5-a]pyrimidine templates have been brought together into a new chemical entity. Ultrasound irradiation of N-(adamantan-1-yl)-3-amino-1H-pyrazole-4-carboxamide with formylated active proton compounds yields the desired hybrids in good to excellent yields. The N-(adamantan-1-yl)-3-amino pyrazolo[1,5-a]pyrimidine carboxamide derivatives were successfully identified with the help of spectral and analytical data. X-ray crystallography of ethyl 3-(adamantan-1-ylcarbamoyl)-7-methylpyrazolo[1,5-a]pyrimidine-6-carboxylate (14c) unambiguously confirmed the formation of the desired hybrid. The results and the findings of the docking scores indicate that the active ligands 7a and 11b exhibited highest binding energies with a score of –7.33 Kcal/mol and – 8.73 Kcal/mol, respectively. The inhibition constant (KI) for ligands 7a and 11b were found to be 4.24 µM and 396.32 µM, respectively which are comparatively lower than the control favipiravir thereby conforming to the drug-likeness prediction. These compounds as such become favorable for screening as drug candidates compared to the control favipiravir with lower binding energy, lower lipophilicity range and very high KI constant. The active ligands have promising functions to inhibit and interfere with the replication and maturation of Chymotrypsin-like protease (3CLpro) of SARS-Coronavirus 2. The lower KI, high binding energy and drug-likeness efficiency of the compounds can be further developed into a potent drug molecule against the uncontrollable SARS-COV-2.

Computer-aided comprehensive explorations of RNA structural polymorphism through complementary simulation methods

While RNA folding was originally seen as a simple problem to solve, it has been shown that the promiscuous interactions of the nucleobases result in structural polymorphism, with several competing structures generally observed for non-coding RNA. This inherent complexity limits our understanding of these molecules from experiments alone, and computational methods are commonly used to study RNA. Here, we discuss three advanced sampling schemes, namely Hamiltonian-replica exchange molecular dynamics (MD), ratchet-and-pawl MD and discrete path sampling, as well as the HiRE-RNA coarse-graining scheme, and highlight how these approaches are complementary with reference to recent case studies. While all computational methods have their shortcomings, the plurality of simulation methods leads to a better understanding of experimental findings and can inform and guide experimental work on RNA polymorphism.Copyright ©

Fight against COVID-19: Functional and structural study of the T cell response

T cells, and especially cytotoxic T cells are at the forefront of the fight against viral infection. The killer cells are able not only to distinguish between self and foreign peptides, but also to engage in the fight to clear the viral infection by eliminating the infected cells. Our lab is focused on understanding how T cells engage with viral peptide antigens, that are presented by highly polymorphic HLA molecules. T cells have receptors on their surface called T cell receptors (TCRs) that allow them to recognize the composite surface of the peptide- HLA complex. Using x-ray crystallography we can understand at the atomic level both peptide antigens presentation and TCR recognition, both important to determine the quality of the subsequent immune response. We can then link that structural information with our cellular assay that determines the strength and magnitude of the anti-viral response, providing the basis for peptide modification to reach stronger response or an understanding of viral mutation that led to viral escape. Our current work compared the T cell response, at the antigen level against 32 single epitope derived from spike, between COVID-19 recovered and vaccinated donors. We have shown that the booster shot (3rd dose) increases the antigen-specific T cell response, increases the level of T cell cross-reactivity against variant of SARS-CoV-2, but also alters the phenotype of the T cell. Those results are important to future guide vaccination advise and better understand the immune response to SARS-CoV-2 infection. POSTER PRESENTATIONS Autoimmunity, Infection, Reproduction and Cancer.

Studying the Effect of Glycosylation towards SARS-CoV-2 Spike RBD and ACE2 Interaction by Native Mass Spectrometry

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has serious consequences on global public health and social development. The binding of receptor binding domain (RBD) of spike protein to angiotensin converting enzyme 2 (ACE2) on the surface of SARS-CoV-2 host cell initiates the infection progress. Spike and ACE2 are both glycoproteins, the impact of glycosylation on protein structures and protein-protein interactions remains largely elusive. Characterizing the structural and dynamics of protein-protein binding progress will improve mechanism understanding of viral infection and facilitate targeted drug design. Structural mass spectrometry (MS) method is widely used in protein structural studies, providing complementary information to conventional biophysical methods, such as X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy and cryo-electron microscopy (cryo-EM). Native mass spectrometry (native MS) is an emerging technology that enables the study of intact protein, non-covalent protein-protein, and protein-ligand complexes in their biological state, which can provide structural stability, binding stoichiometry, and spatial arrangement information. Here, native MS was used to examine the interaction between RBD and ACE2 as well as the impact of deglycosylation on the interaction stability of the RBD-ACE2 complex. The results revealed that both RBD and ACE2 are highly glycosylated, ACE2 presents as a dimer while RBD as a monomer, and they form a (RBD-ACE2)2 complex. The conditions of using PNGasc F to remove the N-glycan were optimized. At least two Oglycans including NcuAc(2) and GalNAcC 1) Gal( 1) NcuAc(2) or GlcNAcd ) Gal(l) NeuAc(2) were observed for the N-glycan removed RBD. Furthermore, the stability of the complexes formed by glycosylated and deglycosylated RBD with ACE2 was compared, and the results showed that the removal of N-glycan significantly drops the interaction stability of the RBD-ACE2 complex. Therefore, we recommend that glycosyla-tion should not be removed for structural and functional studies. Additional glycosyla-tion, structural and dynamics studies on Spike (including separated RBD) and ACE2 complexes would help us to understand the process of viral infection, advance drug design and vaccine developments. Nowadays, a comprehensive MS-based toolbox has been developed for the analysis of protein structure, function, and dynamics, including hydrogen-deuterium exchange MS (HDX-MS), native top-down (nTD) MS, cross-linking MS (XL-MS), and covalent labelling MS (CL-MS), etc. Through integrating structural MS methods, more detailed and comprehensive structural information about glycoproteins and their complexes will be uncovered. © 2022 Chinese Society for Mass Spectrometry. All rights reserved.

Studying the Effect of Glycosylation towards SARS-CoV-2 Spike RBD and ACE2 Interaction by Native Mass Spectrometry

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has serious consequences on global public health and social development. The binding of receptor binding domain (RBD) of spike protein to angiotensin converting enzyme 2 (ACE2) on the surface of SARS-CoV-2 host cell initiates the infection progress. Spike and ACE2 are both glycoproteins, the impact of glycosylation on protein structures and protein-protein interactions remains largely elusive. Characterizing the structural and dynamics of protein-protein binding progress will improve mechanism understanding of viral infection and facilitate targeted drug design. Structural mass spectrometry (MS) method is widely used in protein structural studies, providing complementary information to conventional biophysical methods, such as X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy and cryo-electron microscopy (cryo-EM). Native mass spectrometry (native MS) is an emerging technology that enables the study of intact protein, non-covalent protein-protein, and protein-ligand complexes in their biological state, which can provide structural stability, binding stoichiometry, and spatial arrangement information. Here, native MS was used to examine the interaction between RBD and ACE2 as well as the impact of deglycosylation on the interaction stability of the RBD-ACE2 complex. The results revealed that both RBD and ACE2 are highly glycosylated, ACE2 presents as a dimer while RBD as a monomer, and they form a (RBD-ACE2)2 complex. The conditions of using PNGasc F to remove the N-glycan were optimized. At least two Oglycans including NcuAc(2) and GalNAcC 1) Gal( 1) NcuAc(2) or GlcNAcd ) Gal(l) NeuAc(2) were observed for the N-glycan removed RBD. Furthermore, the stability of the complexes formed by glycosylated and deglycosylated RBD with ACE2 was compared, and the results showed that the removal of N-glycan significantly drops the interaction stability of the RBD-ACE2 complex. Therefore, we recommend that glycosyla-tion should not be removed for structural and functional studies. Additional glycosyla-tion, structural and dynamics studies on Spike (including separated RBD) and ACE2 complexes would help us to understand the process of viral infection, advance drug design and vaccine developments. Nowadays, a comprehensive MS-based toolbox has been developed for the analysis of protein structure, function, and dynamics, including hydrogen-deuterium exchange MS (HDX-MS), native top-down (nTD) MS, cross-linking MS (XL-MS), and covalent labelling MS (CL-MS), etc. Through integrating structural MS methods, more detailed and comprehensive structural information about glycoproteins and their complexes will be uncovered. © 2022 Chinese Society for Mass Spectrometry. All rights reserved.

In Silico Identification of Potential Inhibitors of SARS-CoV-2 Papain-like Protease From Natural Sources: A Natural Weapon to Fight COVID-19

Background: The rapid spread of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) globally has created unprecedented health care and economic crisis. The ever-in-creasing death toll highlights an urgent need for the development of specific antiviral to combat Novel Coronavirus Disease 2019 (COVID-19). Objective(s): In the present study, we aimed to identify potential SARS-CoV-2 papain-like protease inhibitors from regularly used spices. Method(s): A structure-based virtual screening (VS) of our in-house databank of 1152 compounds was employed to identify small molecule inhibitors of SARS-CoV-2 papain-like protease (PLpro), which are important protease for virus replication. The databank was built of the compounds from ten spices and two medicinal plants. Result(s): The top three potential hits that resulted from VS were myricetin (1) available in Alium cepa and Mentha piperita;alpha-hydroxyhydrocaffeic acid (2) available in M. Piperita;and luteolin (3) available in M. Piperita, Curcuma longa, A. cepa, and Trigonella foenum-graecum, which showed fair binding affinity to PLpro of SARS-CoV-2 compared to known SARS-CoV PLpro in-hibitors. The predicted Absorption, Distribution, Metabolism, and Excretion (ADME) properties of the selected hits showed that all are drug-like. The compounds bind to biologically critical regions of the target protein, indicating their potential to inhibit the functionality of this component. Conclusion(s): There are only a few reports available in the literature on the in-silico identification of PLpro inhibitors and most of them used homology modeling of protein. Here, we used the recently uploaded X-ray crystal structure of PLpro (PDB ID: 6WX4) with a well-defined active site. Our computational approach has resulted in the identification of effective inhibitors of SARS-CoV-2PL-pro. The reported edible spices may be useful against COVID-19 as a home remedy after an in--vitro study.Copyright © 2021 Bentham Science Publishers.

Crystal structure of the membrane (M) protein from a bat betacoronavirus.

The membrane (M) protein is the most abundant structural protein of coronaviruses including MERS-CoV, SARS-CoV, and SARS-CoV-2, and plays a central role in virus assembly through its interaction with various partner proteins. However, mechanistic details about how M protein interacts with others remain elusive due to lack of high-resolution structures. Here, we present the first crystal structure of a betacoronavirus M protein from Pipistrellus bat coronavirus HKU5 (batCOV5-M), which is closely related to MERS-CoV, SARS-CoV, and SARS-CoV-2 M proteins. Furthermore, an interaction analysis indicates that the carboxy-terminus of the batCOV5 nucleocapsid (N) protein mediates its interaction with batCOV5-M. Combined with a computational docking analysis an M-N interaction model is proposed, providing insight into the mechanism of M protein-mediated protein interactions.

Teaching Single Crystal X-ray Crystallography in the Undergraduate Classroom with Sugar and Epsom Salt

We developed a single crystal X-ray crystallography experiment based on the crystal structure of sucrose (table sugar), and a more challenging experiment using Epsom salt. Both crystals are readily available in X-ray quality crystalline form. In these experiments, students mounted a crystal on a MiTeGen loop and analyzed it using a Rigaku XtaLAB Mini diffractometer (built 2011). Students generated models of both compounds using CrysAlisPro, Olex2, SHELXT, and SHELXL. All aspects of this experiment use free software programs which have user-friendly interfaces. A step-by-step laboratory protocol for determining the structure of both compounds is included in the Supporting Information. These experiments were used in the Fall of 2019 at the Junior and the Senior level. In the Summer of 2020, a take-home version of the lab was created in response to the Novel 2019 Coronavirus (COVID-19) pandemic and implemented in the General Chemistry laboratory curriculum;this experiment was used for the duration of the 2020-2021 academic year. These experiments are suitable for all undergraduate experience levels. © 2022 American Chemical Society and Division of Chemical Education, Inc.

Structural insights into protection against a SARS-CoV-2 spike variant by T cell receptor diversity.

T cells play a crucial role in combatting SARS-CoV-2 and forming long-term memory responses to this coronavirus. The emergence of SARS-CoV-2 variants that can evade T cell immunity has raised concerns about vaccine efficacy and the risk of reinfection. Some SARS-CoV-2 T cell epitopes elicit clonally restricted CD8+ T cell responses characterized by T cell receptors (TCRs) that lack structural diversity. Mutations in such epitopes can lead to loss of recognition by most T cells specific for that epitope, facilitating viral escape. Here, we studied an HLA-A2-restricted spike protein epitope (RLQ) that elicits CD8+ T cell responses in COVID-19 convalescent patients characterized by highly diverse TCRs. We previously reported the structure of an RLQ-specific TCR (RLQ3) with greatly reduced recognition of the most common natural variant of the RLQ epitope (T1006I). Opposite to RLQ3, TCR RLQ7 recognizes T1006I with even higher functional avidity than the WT epitope. To explain the ability of RLQ7, but not RLQ3, to tolerate the T1006I mutation, we determined structures of RLQ7 bound to RLQ-HLA-A2 and T1006I-HLA-A2. These complexes show that there are multiple structural solutions to recognizing RLQ and thereby generating a clonally diverse T cell response to this epitope that assures protection against viral escape and T cell clonal loss.

Computational tools for aptamer identification and optimization

Aptamers are single-stranded DNA or RNA oligonucleotides that can selectively bind to a specific target. They are generally obtained by SELEX, but the procedure is challenging and time-consuming. Moreover, the identified aptamers tend to be insufficient in stability, specificity, and affinity. Thus, only a handful of aptamers have entered the practical use stage. Recently, computational approaches have demonstrated a significant capacity to assist in the discovery of high-performance aptamers. This review discusses the advances achieved in several aspects of computational tools in this field, as well as the new progress in machine learning and deep learning, which are used in aptamer identification and optimization. To illustrate these computationally aided processes, aptamer selections against SARS-CoV-2 are discussed in detail as a case study. We hope that this review will aid and motivate researchers to develop and utilize more computational techniques to discover ideal aptamers effectively. Copyright © 2022 Elsevier B.V.

Revealing druggable cryptic pockets in the Nsp1 of SARS-CoV-2 and other ß-coronaviruses by simulations and crystallography.

Non-structural protein 1 (Nsp1) is a main pathogenicity factor of α- and ß-coronaviruses. Nsp1 of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) suppresses the host gene expression by sterically blocking 40S host ribosomal subunits and promoting host mRNA degradation. This mechanism leads to the downregulation of the translation-mediated innate immune response in host cells, ultimately mediating the observed immune evasion capabilities of SARS-CoV-2. Here, by combining extensive molecular dynamics simulations, fragment screening and crystallography, we reveal druggable pockets in Nsp1. Structural and computational solvent mapping analyses indicate the partial crypticity of these newly discovered and druggable binding sites. The results of fragment-based screening via X-ray crystallography confirm the druggability of the major pocket of Nsp1. Finally, we show how the targeting of this pocket could disrupt the Nsp1-mRNA complex and open a novel avenue to design new inhibitors for other Nsp1s present in homologous ß-coronaviruses.

New Cu(II), Mn(II) and Mn(III) Schiff base complexes cause noncovalent interactions: X-ray crystallography survey, Hirshfeld surface analysis and molecular simulation investigation against SARS-CoV-2.

In this study, polynuclear Cu(II) complex (1), Mn(II) and Mn(III) complex (2) have been prepared with a Schiff base ligand derived from 2-Hydroxy-3-methoxybenzaldehyde with 2-amino-2-methyl-1-propanol. The compounds were characterized by elemental analysis, FT-IR, and UV-Vis spectroscopy. The molecular and crystal structures of (1-2) were determined by the single-crystal x-ray diffraction technique. It turned out that Cu(II) complex (1) forms an S4 -symmetrical tetrameric cage structure, with square-planar coordinated Cu and bridging O atoms at the vertexes of the approximate cube. In the crystal structure of 1, there are large channels along the c-axis, between the tetramers; the solvent- DMSO molecules, occupies these channels. In turn, the complex (2) creates a centrosymmetric trimeric structure, with three octahedrally coordinated Mn ions bridged by O atoms from ligand molecules and acetate ions. The electrochemical behavior studies of the complexes in DMSO displayed the electronic effects of the groups on the redox potential. The redox behavior of Schiff base (1) and (2) complexes included quasi -reversible and irreversible voltammograms, respectively. Intermolecular interactions in the solid states were studied by Hirshfeld surface analysis. These studies provide a comprehensive description of these inter-contact exchanges using an attractive graphical representation using Hirshfeld surfaces and fingerprint plots, along with enrichment ratios. Furthermore, assessment of the inhibitory effect against coronavirus (main protease SARS-CoV-2) was performed by a molecular docking study for both complexes (1 and 2). Both complexes showed a good affinity for CoV-2 for PDB protein ID: 6M03 and 6Y2F.

Unmasking the Conformational Stability and Inhibitor Binding to SARS-CoV-2 Main Protease Active Site Mutants and Miniprecursor.

We recently demonstrated that inhibitor binding reorganizes the oxyanion loop of a monomeric catalytic domain of SARS CoV-2 main protease (MPro) from an unwound (E) to a wound (active, E*) conformation, independent of dimerization. Here we assess the effect of the flanking N-terminal residues, to imitate the MPro precursor prior to its autoprocessing, on conformational equilibria rendering stability and inhibitor binding. Thermal denaturation (Tm) of C145A mutant, unlike H41A, increases by 6.8 °C, relative to wild-type mature dimer. An inactivating H41A mutation to maintain a miniprecursor containing TSAVL[Q or E] of the flanking nsp4 sequence in an intact form [(-6)MProH41A and (-6*)MProH41A, respectively], and its corresponding mature MProH41A were systematically examined. While the H41A mutation exerts negligible effect on Tm and dimer dissociation constant (Kdimer) of MProH41A, relative to the wild type MPro, both miniprecursors show a 4-5 °C decrease in Tm and > 85-fold increase in Kdimer as compared to MProH41A. The Kd for the binding of the covalent inhibitor GC373 to (-6*)MProH41A increases ∼12-fold, relative to MProH41A, concomitant with its dimerization. While the inhibitor-free dimer exhibits a state in transit from E to E* with a conformational asymmetry of the protomers' oxyanion loops and helical domains, inhibitor binding restores the asymmetry to mature-like oxyanion loop conformations (E*) but not of the helical domains. Disorder of the terminal residues 1-2 and 302-306 observed in both structures suggest that N-terminal autoprocessing is tightly coupled to the E-E* equilibrium and stable dimer formation.

Rational design of the zonulin inhibitor AT1001 derivatives as potential anti SARS-CoV-2.

Although vaccines are greatly mitigating the worldwide pandemic diffusion of SARS-Cov-2, therapeutics should provide many distinct advantages as complementary approach to control the viral spreading. Here, we report the development of new tripeptide derivatives of AT1001 against SARS-CoV-2 Mpro. By molecular modeling, a small compound library was rationally designed and filtered for enzymatic inhibition through FRET assay, leading to the identification of compound 4. X-ray crystallography studies provide insights into its binding mode and confirm the formation of a covalent bond with Mpro C145. In vitro antiviral tests indicate the improvement of biological activity of 4 respect to AT1001. In silico and X-ray crystallography analysis led to 58, showing a promising activity against three SARS-CoV-2 variants and a valuable safety in Vero cells and human embryonic lung fibroblasts. The drug tolerance was also confirmed by in vivo studies, along with pharmacokinetics evaluation. In summary, 58 could pave the way to develop a clinical candidate for intranasal administration.

Neutralizing monoclonal antibodies elicited by mosaic RBD nanoparticles bind conserved sarbecovirus epitopes.

Increased immune evasion by SARS-CoV-2 variants of concern highlights the need for new therapeutic neutralizing antibodies. Immunization with nanoparticles co-displaying spike receptor-binding domains (RBDs) from eight sarbecoviruses (mosaic-8 RBD-nanoparticles) efficiently elicits cross-reactive polyclonal antibodies against conserved sarbecovirus RBD epitopes. Here, we identified monoclonal antibodies (mAbs) capable of cross-reactive binding and neutralization of animal sarbecoviruses and SARS-CoV-2 variants by screening single mouse B cells secreting IgGs that bind two or more sarbecovirus RBDs. Single-particle cryo-EM structures of antibody-spike complexes, including a Fab-Omicron complex, mapped neutralizing mAbs to conserved class 1/4 RBD epitopes. Structural analyses revealed neutralization mechanisms, potentials for intra-spike trimer cross-linking by IgGs, and induced changes in trimer upon Fab binding. In addition, we identified a mAb-resembling Bebtelovimab, an EUA-approved human class 3 anti-RBD mAb. These results support using mosaic RBD-nanoparticle vaccination to generate and identify therapeutic pan-sarbecovirus and pan-variant mAbs.

Structural basis for mouse receptor recognition by SARS-CoV-2 omicron variant.

The sudden emergence and rapid spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) omicron variant has raised questions about its animal reservoir. Here, we investigated receptor recognition of the omicron's receptor-binding domain (RBD), focusing on four of its mutations (Q493R, Q498R, N501Y, and Y505H) surrounding two mutational hotspots. These mutations have variable effects on the RBD's affinity for human angiotensin-converting enzyme 2 (ACE2), but they all enhance the RBD's affinity for mouse ACE2. We further determined the crystal structure of omicron RBD complexed with mouse ACE2. The structure showed that all four mutations are viral adaptations to mouse ACE2: three of them (Q493R, Q498R, and Y505H) are uniquely adapted to mouse ACE2, whereas the other one (N501Y) is adapted to both human ACE2 and mouse ACE2. These data reveal that the omicron RBD was well adapted to mouse ACE2 before omicron started to infect humans, providing insight into the potential evolutionary origin of the omicron variant.

The tem-per-ature-dependent conformational ensemble of SARS-CoV-2 main protease (Mpro).

The COVID-19 pandemic, instigated by the SARS-CoV-2 coronavirus, continues to plague the globe. The SARS-CoV-2 main protease, or Mpro, is a promising target for the development of novel antiviral therapeutics. Previous X-ray crystal structures of Mpro were obtained at cryogenic tem-per-ature or room tem-per-ature only. Here we report a series of high-resolution crystal structures of unliganded Mpro across multiple tem-per-atures from cryogenic to physiological, and another at high humidity. We inter-rogate these data sets with parsimonious multiconformer models, multi-copy ensemble models, and isomorphous difference density maps. Our analysis reveals a perturbation-dependent conformational landscape for Mpro, including a mobile zinc ion inter-leaved between the catalytic dyad, mercurial conformational heterogeneity at various sites including a key substrate-binding loop, and a far-reaching intra-molecular network bridging the active site and dimer inter-face. Our results may inspire new strategies for antiviral drug development to aid preparation for future coronavirus pandemics.

Different phosphoric triamide [HN]3-nP(O)[N]n (n = 1, 2) skeletons lead to identical non-covalent interactions assemblies: X-ray crystallography investigation, Hirshfeld surface analysis and molecular docking study against SARS-CoV-2

In this work, we describe the crystal structures of two new phosphoramides containing the same [(3-Cl)C6H4NH]P(O) = Y segment (Y[N(CH3)CH2C6H5]2 (1) and Y[NC4H8O]2 (2)) and an improved model of [C6H11(CH3)N]P(O)[NHC(CH3)3]2 (compound 3). The structures are experimentally investigated by single crystal X-ray diffraction using two types of refinements with spherical (S) and aspherical (AS) [Hirshfeld atomic refinements (HARs)] form factors, FT-IR and 1H, 13C, 31P NMR spectroscopy. A biological molecular docking investigation gives hints to suggest an appropriate inhibitory activity against MPro of SARS-COV-2 (6M03 and 6LU7) especially for 1 with a binding energy around −6 (6M03)/−7 (6LU7) kcal/mol. In the present work, the docking simulations are carried out for the first time for three series of ligand (L)-protein (P) complexes: L (with S form)-P (6M03), L (with AS form)-P (6M03) and L (AS)-P (6M03-N, with hydrogen atoms at their theoretical neutron values), where the binding energies are approximately proved to be 0.8 kcal/mol lower for simulations with 6M03-N than those for 6M03. Moreover, the structural study illustrates that the hydrogen bond patterns of all three structures consist of one-dimensional zigzag chains formed by classical NH…O hydrogen bond interactions. Further stabilization is provided by weak interactions such as CH…Cl (for 1 and 2), Cl…π (for 1 and 2) and CH…O (for 2 and 3). Furthermore, the intermolecular interactions are analyzed by three-dimensional (3D) Hirshfeld surfaces, 2D fingerprint plots and enrichment ratios. The favored contacts identified by Hirshfeld surface analysis are H…O/O…H interactions covering the NH…O hydrogen bonds for all three structures. For 1 and 2, Cl…C/C…Cl contacts covering Cl…π interactions are recognized as the most enriched contacts.